Various combustion chamber configurations for direct injected, reciprocating piston, spark and compression ignited internal combustion engines are known and have been described in literature. Combustion chambers and associated chambers for generating radicals and intermediate species of fuel compounds used during combustion of fuel, or for timed autoignition of fuel charges, also have been described. One type of piston for use in such combustion chamber includes a central bowl for receiving the major portion of each fuel and air charge of each combustion cycle. A fuel injector is commonly utilized to inject the fuel of each charge towards the piston bowl in such a combustion chamber configuration, and the bowl communicates with associated micro chambers in the piston or cylinder head via orifices or ports.
A piston arrangement for achieving improved control over ignition and combustion characteristics of a fuel charge in an internal combustion engine and a process for same achieved by the generation and management of fuel radical species within the combustion chamber of such an engine is described in U.S. Pat. Nos. 4,898,135 to Failla et al., 5,862,788 to Pouring et al., and 6,178,942 to di Priolo et al., each of which is incorporated herein by reference in their entirety. These patents disclose using one or more small “reaction chambers” located adjacent the piston bowl which communicate with the bowl through openings or ports that may be configured as slots or discrete orifices. The orifices are configured to produce a lag between gaseous flow of fuel and air (possibly mixed with prior combustion products) into the reaction chamber and the discharge of partially reacted fuel radicals and intermediate species from the reaction chamber into the piston bowl. Reference may be made to the above-mentioned patents for a fuller discussion of radical enhanced combustion and radical induced ignition in reciprocating internal combustion engines.
During each combustion cycle, the portion of the air/fuel charge that is forced into the reaction chamber during combustion and compression phases of a first or an earlier combustion cycle undergoes a cool flame oxidation process to produce fuel radicals and intermediate species that are available for discharge into the bowl of the piston and the combustion chamber above the piston in a next succeeding combustion cycle for seeding the next air/fuel charge provided in the combustion chamber in accordance with a timed process to achieve various objectives, including, for example, more complete combustion, exhaust gas clean-up, autoignition of the charge, etc.
FIG. 1 schematically illustrates an exemplary prior art combustion chamber configuration for a direct injected, compression-ignition, reciprocating piston internal combustion engine 100 using a piston 105 having an annular top side crown or cap 110 fastened to an upper side of the piston body 105. The annular cap 110 has reaction chambers 130, i.e., micro chambers, for containing and generating fuel radical species located in circumferentially spaced relationship about piston bowl 120. The annular cap 110 is configured to adjust the compression ratio of the illustrated combustion chamber above the piston 105. For example, for a lower compression ratio, the volume of the piston bowl 120 would be increased to provide a greater free volume above the piston for the combustion process.
The micro chambers 130 in the prior art piston are formed on the bottom side of the cap 110, which are fastened to the piston body by mechanical fasteners such as bolts. This configuration was necessitated apparently because it was not clear how the micro chambers could be integrated in the main piston body without adversely affecting the structural integrity of the piston.
The use of the cap thus was a necessary expedient to provide micro chambers adjacent the combustion bowl of the combustion chamber with ports between the chambers and the bowl to provide communication between the bowl and the chambers. However, the assembly of a cap on a piston resulted in a piston that was structurally unsound and that would ultimately fail over time due to the stresses of the combustion process. Machining micro chambers in the bowl side wall or providing chambers in the side wall during piston manufacturing also was impractical and costly.
The outer boundary of the reaction chambers 130 obviously encroaches on the backside of any adjacent piston ring recess 140, resulting in a small thickness of piston material between the micro chamber 130 and adjacent piston ring recess 140. Since the overall thickness between the reaction chambers 130 and side wall 150 of the cap is already low, the further encroachment resulting from increasing the volume of the piston bowl 120 leaves a small amount of piston body material to receive a fastener to retain the annular cap 110 on the piston body. This results in a weakened area of the cap adjacent the micro chambers.
The small, i.e., thin, thickness between piston reaction chambers 130 and piston ring recess 140 limits the piston integrity. This leads to problems when fabricating a piston head having a piston bowl 120, reaction chambers 130, and piston ring recess 140.
The present invention resulted from the recognition that there is a need for a process to produce a piston of the type shown in FIG. 1 with a central bowl and micro chambers in the bowl sidewalls that do not require fastening a separate cap fastened on the upper side of a piston body to obtain the micro chambers. Such process must be inexpensive to implement and must result in a structurally sound piston that can withstand the rigors of the combustion cycle of an engine over the life of the piston, while at the same time enabling production of micro chambers in the piston having various volumes and geometrical configurations to accommodate various radical production schemes and the use of the fuel radicals to enhance combustion and/or ignition of the fuel charge in the bowl of the combustion chamber.